1. Technical Field of the Invention
The present invention relates to a sound generation apparatus using a serial flash memory having a small number of terminals.
2. Description of the Related Art
A so-called waveform memory tone generator for generating a musical sound signal is well known from the past. The waveform memory tone generator reads waveform data from a waveform memory according to a musical sound generation instruction to generate a musical sound signal. Various kinds of memory devices, such as a read only memory (ROM), a flash memory, and a random access memory (RAM), are used as the waveform memory for storing waveform data.
Patent Literature 1 discloses a one-chip tone generator LSI including a CPU and a tone generating unit provided therein. To the tone generator LSI is connected a read only memory for storing a program executed by the CPU and waveform sample data used for the tone generating unit to generate a musical sound. The tone generating unit generates musical sounds by a plurality of channels (ch) through time division processing. In a time slot of each channel, therefore, the tone generating unit performs an access to the read only memory through a parallel bit address having a plurality of bits and reads waveform samples, which are parallel bit data having a plurality of bits. At the same time, the CPU executes various control operations. Consequently, the CPU performs an access to the read only memory through a parallel bit address having a plurality of bits and reads program instructions of a control program, which are also parallel bit data having a plurality of bits.
On the other hand, a so-called serial flash memory (hereinafter, occasionally referred to as a ‘serial flash’) is well known as a semiconductor memory device. The serial flash memory can reduce a pattern area of a circuit board and can reduce the number of wires (for example, see Non-Patent Literature 1 below). The serial flash is a memory device wherein the number of terminals (pins) is small and each pin has a plurality of functions. For example, the serial flash may include 8 pins, such as a power supply pin VCC, a ground pin GND, a pin for a chip select signal CS, a pin for a clock signal CLK, and data input and output pins IO1 to IO4. It is possible for the serial flash to read data in several different manners according to a set mode or a designated instruction. In addition, the serial flash has a small number of pins and thus requires a reduced number of wires.
Consequently, it is possible to reduce the area of the serial flash mounted on the board.
[Patent Literature 1] Japanese Patent No. 3152198
[Non-Patent Literature 1] http://www.winbond.com/hq/enu/ProductAndSales/ProductLines/FlashMemory/SerialFlash/W25Q64BV.htm
In the conventional waveform memory tone generator as described above, a memory having a large number of pins constituting address terminals and data input and output terminals is used as the waveform memory for storing waveform sample data. As a result, the chip sizes of the tone generator LSI and the waveform memory are increased and thus the number of wires therebetween is increased. Consequently, the areas of the tone generator LSI and the waveform memory mounted on a circuit board are increased with the result that it is necessary to provide a large-sized printed circuit board. In order to reduce the chip sizes of the tone generator LSI and the waveform memory and to configure the circuit board to have a compact structure, it may be considered to store waveform data in the serial flash having a small number of pins as described above. However, the serial flash serially reads data with the result that read speed is slow. For this reason, the serial flash generally reads waveform sample data with the result that the available number of tone generating channels is small.
Particularly, in an electronic musical instrument of a type that stores waveform sample data and a program executed by a CPU in the read only memory as disclosed in Patent Literature 1 described above, the program is read by the CPU simultaneously when the waveform sample data are read with the result that read speed of the waveform sample data is further reduced.